Steady state kinetic model for entrained flow CO₂ gasification of biomass at high temperature

Entrained flow gasification technology is considered as a promising technology for its unique nature; high carbon conversion in short residence time and fewer pollutants emission for utilizing solid fuels towards high-value products. In a two-stage dry feed entrained flow gasifier, CO₂ is the predominant gas species that evolves from combustion zone with a concentration around 77% and 18% during oxy and air-fired gasifier respectively. The CO₂ rich gas stream acts as a reactant in the reduction zone that produces syngas. This article presents a kinetic model of CO₂ gasification of biomass that mimics the reduction zone of a dry feed entrained flow reactor. The model is based on plug flow analogy for heat and mass balance. Explicit calculations are performed to calculate particle residence time. Gas-phase reactions are introduced, and the predicted results are compared against a bench-scale entrained flow reactor. The results indicate during high-temperature CO₂ gasification condition; the gas-phase chemistry is dominated by the homogenous reverse water gas shift reaction (rWGSR). Particle structure plays an essential role by imposing diffusional effects during char conversion. An increased concentration of CO₂ served a dual purpose: raising devolatilization rate and lowering the diffusional limitation.